This invention is concerned with a technique for providing a wellbore that extends from a surface location into the earth's crust and through formations thereof to a subsurface location in a mineral bearing formation which subsurface location is spaced a great lateral distance from the surface location.
Wellbores and wells have been extended into the earth in directions other than vertical for various reasons and by various techniques. A need for such wells was early recognized and still exists today for tapping mineral reserves located beneath water bodies or located beneath other poorly accessible surface locations. For example, before the turn of the century, the Summerland Field, located underwater near Santa Barbara, Calif., was drilled by whipstocking holes out under the water from land locations.
In U.S. Pat. No. 3,285,350 to J. K. Henderson, there is described a technique for drilling off-vertical holes through earth formations and more particularly a technique and apparatus for controllably drilling holes through and substantially parallel to mineral formations between separated wells.
In U.S. Pat. No. 2,778,603 to McCune et al., there is described a method and apparatus for lining wellbores, such as bores extending laterally or generally horizontally from a main bore into a surrounding formation. In U.S. Pat. No. 3,933,447 to Pasini et al., there is described a method for the gasification of coal in situ. In one aspect there described, a borehole is drilled from the earth's surface preferably on a slant so as to intersect the coal bed while traveling in a horizontal direction. Using this technique, it was found that major advantages are achieved over the use of vertical wells or blind boreholes. In U.S. Pat. Nos. 3,986,557 and 4,007,788 both to Striegler et al., there are described methods of producing bitumen from subterranean tar sand formations which methods employ a continuous wellbore having a second section thereof contained within the formation and a first and a third section extending said second section to the earth's surface.